Precursor conditions to Alzheimer's disease (AD) such as Mild Cognitive Impairment (MCI) are now a target of patient identification and potential treatment, as studies clearly showing that the risk of progression to dementia is very high. Despite attempts to develop new treatments for AD and its precursor, MCI, methods of interrupting the course of illness and preventing progression have proven elusive. Treatment strategies for AD based on molecular pathologies (such as A) have thus far produced equivocal or negative results. Investigation is thus shifting to the potential treatment of precursr conditions, including MCI, pre-MCI, and subjects at risk with identification via genetics or other biomarkers. Losses of cholinergic neurons and particularly nicotinic cholinergic receptors have been shown to be principally related to cognitive decline in AD. However, approved treatments for AD have not significantly improved MCI, despite clear evidence of alteration of cholinergic function at this stage, Thus nonspecific enhancement of cholinergic function does not appear to be a fruitful strategy for either enhancing long-term cognitive functioning in MCI, nor retarding the progression to AD. There is a continuing search for new treatments that will improve cognitive symptoms while potentially be disease modifying. Nicotine may be one of those molecules and is easily available, inexpensive, and easy to use. We have performed a double-blind 6 month pilot trial showing that nicotine treatment significantly improved cognitive performance in the areas of attention and episodic memory, showed improving global ratings of functioning and self-rated memory problems, and was well tolerated with an impressive safety profile and no abuse liability (Newhouse, P., K. Kellar, et al. (2012). Neurology 78(2): 91-101). We now propose a definitive 2-year multi-center clinical trial to test whether daily transdermal nicotine will produce sustained cognitive, clinical, and functional benefits in patients with MCI. Our primary hypothesis is that transdermal nicotine will enhance cognitive performance and symptoms of cognitive dysfunction compared to placebo and that this difference will be sustained over two years. We also plan to test in a smaller sub study whether there is evidence that nicotine treatment will affect the underlying biology related to MCI/AD by monitoring biological markers including structural and functional brain imaging and measures of AD pathology in spinal fluid. This proposed study has broad clinical and scientific significance. If the hypotheses were validated, these findings would support a novel, broadly available, and inexpensive intervention for MCI and would encourage early treatment intervention to improve symptoms and/or retard progression of cognitive impairment. This would be the longest trial of nicotine or nicotinic agonists to date and if successful would lead to combined trials with other symptomatic agents and/or agents that might directly interact with A or tau- related mechanisms.